It is known to manufacture polyesters from furandicarboxylic acid or esters thereof and a diol. In this respect reference is made to GB 621971, wherein the preparation of polyesters has been described. In this preparation a glycol is reacted with dicarboxylic acids of which at least one contains a heterocyclic ring. As an example of such a dicarboxylic acid, 2,5-furandicarboxylic acid is mentioned.
EP 294863 describes aromatic polyesters that have liquid crystalline properties. The aromatic polyesters are characterised in that they contain heterocyclic units with two carbonyl groups. The heterocyclic unit may be derived from 2,5-furandicarboxylic acid, 2,4-furandicarboxylic acid, 2,3-furandicarboxylic acid or derivatives of these acids.
In US 2009/0124763 a polymer compound is provided that is the polymerisation product of a furandicarboxylic acid and a diol, and that has a polymerisation degree of 185 to 600. The polymer compound is stated to have excellent mechanical strength. The polymer compound that is exemplified contains 2,5-furandicarboxylate moieties and divalent hydrocarbon groups. Suitable hydrocarbon groups include alkylene groups with 2 to 5 carbon atoms. The polymer thus provided is used as structural material for ink tanks or toner containers or material for copiers, printers or cameras.
A process for the production of furandicarboxylic acids has been described in US 2007/0232815. According to this document furandicarboxylic acid can be prepared by the oxidation of a furan ring compound having two functional groups selected from a hydroxymethyl group, a formyl group and a carboxyl group with a metal permanganate in an alkaline environment. Alternative processes have been discussed in the opening paragraphs of this document. 5-Hydroxymethylfurfural appears to be a suitable starting compound for all processes. 2,5-Furandicarboxylic acid is stated to be a valuable intermediate for pharmaceuticals, agrochemicals, fragrances and so forth.
US 2009/0156841 teaches the production of 5-hydroxymethylfurfural by contacting a carbohydrate source with a solid phase catalyst. Agricultural raw material such as cellulose, starch, sucrose or inulin, can be used as starting material for the production of sugars such as hexoses and pentoses. These sugars are suitable carbohydrate sources for the production of 5-hydroxymethyl furfural. US 2009/0156841 further teaches that a mixture of hydroxymethylfurfural and one or more hydroxymethylfurfural esters may be oxidized to the corresponding furandicarboxylic acid by the addition of an organic acid, cobalt acetate, manganese acetate and sodium bromide under pressure.
From the above state of the art it is evident that furan dicarboxylate containing polyester can be prepared from natural sources. This represents a significant advantage over the production of other polymers that are usually obtained from derivatives of crude oil and other fossil fuels. In order to optimise the environmental friendliness of furan dicarboxylate containing polyester it would be advantageous if such compounds could be re-used. To enable such re-use the present inventors have identified the need to depolymerise furan dicarboxylate containing polyester and to recover the starting materials. This would enable the skilled person to apply the starting materials for any use that would be most advantageous for the skilled person, thus providing a very versatile process.
EP693527 discloses a method for the degradation of unsaturated polyesters using glycol and a catalyst, e.g. an sodium ethanolate. Also in JP 2004 250414 a method is described wherein monomers of polyesters are recovered by solvolysis of the polyester using a monohydric alcohol and a base. WO 2004/060987 discloses a method for the depolymerisation of polyesters and polyamides using a specific carbene catalyst. In an example polyethyleneterephthalate (PET) is depolymerised using 1,3-dimethylimidazole, iodide salt, and potassium tert-butanolate. None of the above references describes that the selection of the polyester results in a difference in depolymerisation behaviour. In EP 857714 the depolymerisation of polyethylene-naphthalenedicarboxylate (PEN) has been described. In this application it is taught that experience in recovering monomers from PET cannot directly be translated to recovery of monomers from PEN.